1. Field of the Invention
This invention relates generally to a hermetic feedthrough terminal pin assembly, preferably of the type incorporating a filter capacitor. More specifically, this invention relates to terminal pins comprising palladium or palladium alloys for incorporated into feedthrough filter capacitor assemblies, particularly of the type used in implantable medical devices such as cardiac pacemakers, cardioverter defibrillators, and the like, to decouple and shield internal electronic components of the medical device from undesirable electromagnetic interference (EMI) signals. The terminal pin feedthrough assembly provides a hermetic seal that prevents passage or leakage of fluids into the medical device.
2. Prior Art
Feedthrough assemblies are generally well known in the art for use in connecting electrical signals through the housing or case of an electronic instrument. For example, in an implantable medical device, such as a cardiac pacemaker, defibrillator, or neurostimulator, the feedthrough assembly comprises one or more conductive terminal pins supported by an insulator structure for passage of electrical signals from the exterior to the interior of the medical device. The conductive terminals are fixed into place using a gold brazing process, which provides a hermetic seal between the pin and insulative material. Conventionally, the terminal pins have been composed of platinum or a combination of platinum and iridium. Platinum and platinum-iridium alloys are biocompatible and have good mechanical strength, which adds to the durability of the feedthrough. However platinum is a precious metal that creates a manufacturing cost barrier.
The replacement of platinum and platinum alloys by palladium and its alloys offers several advantages. First, platinum has a density of 21.45 grams/cc. Palladium has a density of 12.02 grams/cc. These materials are priced by weight, but used by volume, which means that palladium has a significant cost advantage over platinum. Secondly, platinum and palladium have nearly equivalent mechanical properties. After high temperature brazing, there is no significant degradation in the mechanical properties of palladium, such as in strength and elongation, in comparison to platinum. Palladium also has comparable soldering and welding characteristics, and it has good radiopacity. Finally, previous research indicates that palladium is biocompatible under both soft tissue and bone studies. Palladium and additive materials that are typically combined with it to form alloys are regarded as chemically inactive.